Conductive metal-filled substrates via developing agents

ABSTRACT

A conductive metal-filled substrate is formed by intermingling copper or nickel particles into the substrate, contacting the metal particles with a specified developing agent, and heating the metal particles and the developing agent. The filled substrates are electrically conductive and are useful for a variety of uses such as EMI shielding.

BACKGROUND OF THE INVENTION

This invention relates to the formation of substrates which contain afiller such that the filled substrate is rendered electricallyconductive. In particular, this invention relates to such a processwherein the conductive filler is formed from discrete metal particles ofcopper or nickel.

It is frequently desired to incorporate a conductive metal filler in a(generally) non-conductive substrate. Such composites are useful forelectromagnetic interference (EMI) shielding and so forth.

Applicants' co-pending application titled Conductive Metallization ofSubstrates Ser. No. 068,593, and the art cited therein, deals with theproblem of forming a layer of conductive metal on the surface of asubstrate. In contrast, the instant invention deals with the problem ofrendering an entire three-dimensional substrate conductive.

SUMMARY OF THE INVENTION

In one aspect the invention is a method of forming a metal-filledconductive substrate in which the metal particles are incorporated intothe substrate, contacted with a developer, and heated.

In another aspect the invention is a filled substrate made by the abovemethod.

The method of the invention is convenient to carry out, involvesrelatively non-corrosive materials, and produces coherent, veryconductive metal-filled substrates.

DETAILED DESCRIPTION OF THE INVENTION

One element of the invention is the use of nickel or copper particles.In general, any nickel or copper which is in the form of a powder issuitable for use in the invention. Of some importance is the particlesize of the nickel or copper. The principal difficulty with largeparticle sizes is that of obtaining a uniform distribution of particlesin the substrate and ensuring adequate particle-to-particle contact inthe three dimensions of the substrate. Generally, the particle size willbe below 30, preferably below 20, and more preferably below 10 um.

The copper or nickel need not be particularly pure and in factsignificant amounts (e.g. up to 70%) of oxides may be present. Further,mixtures of copper or nickel with other metals may be used. Whenmixtures are used, the mixture is desirably at least 40, more desirablyat least 50, preferably at least 60, and most preferably at least 70weight % copper and/or nickel.

The metal particles are distributed in a substrate. Suitable substratesinclude virtually any material which is capable of temporarily being ina relatively soft, deformable state so as to be able to intermingle themetal powder into its volume and is capable of being in a relativelyhard, non-deformable state so as to be able to provide a relativelyundisturbed distribution of the metal after the metal has becomeintermingled. Thus, materials such as glass, natural resins (e.g.:unvulcanized natural rubber), and synthetic resins are suitable, withsynthetic resins being preferred.

For purposes of the invention, suitable synthetic resins may be dividedinto two categories; thermoplastic resins and uncured resins.Thermoplastic resins are typically employed by powder blending or meltblending the metal powder into the resin. "Uncured" resins are typicallyemployed by providing them in a completely uncured or semi- cured state(sufficiently uncured that the metal particles can intermingle with theresin), mixing the metal particles with the resin, and curing the resinto cause it to harden.

Suitable thermoplastic resins include polyolefins such as polyethylene,polypropylene and polybutadiene; halogenated polyolefins such aspolyvinlidenedifluoride (PVDF); styrenics such as polystyrene, highimpact polystyrene (HIPS), acrylonitrile butadiene-styrene (ABS), andstyrene-acrylonitrile (SAN); acrylics such as polymethylmethacrylate(Plexiglass); polyaryl ethers such as polyphenylene oxide (Noryl);polyamides such as nylon 6; and polyesters such aspolybutyleneterephtholate (PBT). The resins may optionally containfillers such as glass fibers.

Exemplary "uncured" resins include thermoset resins such as epoxy,unsaturated polyester, and silicone rubber. Other uncured (orsemi-cured) resins such as UV cure, electron beam cure, and ionizingradiation cure resins may also be employed. The presence of the metal,however, means that complete curing by these means can only take placein relatively thin layers.

The substrates are illustratively formed into thin (e.g.: 0.5 to 1 mm)sheets but other forms (e.g.: cubes, spheres, etc.) would be suitable.The substrates may be selected from the usual commercial grades ofavailable materials, and no special handling or treatment is required.

It is a requirement of the invention that the metal particles arecontacted with a developing agent. Suitable developing agents includetertiary amines, tertiary phosphorus compounds, and bifunctionalcompounds having both (a) a first atom which is a trivalent nitrogen ora bivalent sulfur and (b) at least one second atom which is nitrogen oroxygen, the first and second atoms being separated by at least two otheratoms (preferably carbon); the bifunctional compound (1) being capableof forming a coordination complex (preferably a chelation complex) withcopper or nickel. It is preferred that the developing agents be ofsufficiently high molecular weight that evaporation of the developingagent at the developing temperature does not interfere with the processof the invention. Generally, a molecular weight of at least 150 ispreferred and a molecular weight of at least 250 is more preferred. Verylow molecular weight compounds may also have a tendency to pit thesubstrate.

Exemplary tertiary amines include long-chain aliphatic tertiary aminessuch as methyldicocoamine and dimethylcocoamine, and tertiary amineswhich may contain a degree of unsaturation such as dimethyltallowamine.

Tertiary amines can be generated in situ by the use of a quaternaryammonium salt, provided that the developing temperature is sufficientlyhigh that the salt thermally degrades to a tertiary amine. Thus,compounds such as dicocodimethylammonium chloride andN,N,N',N',N'-pentamethyl-N-tallow-1,3-propanediammonium dichloride maybe used for in situ generation of tertiary amines. This approach has thedrawback, however, that the counter ions (e.g.: chloride ions) can causecorrosion.

Suitable tertiary phosphorous compounds (P (III) compounds) includetertiary phosphines such as triphenylphosphine (triphenylphosphorous,(C₆ H₅)₃ P) and tertiary phosphites such as tributyl phosphite (CH₃(CH₂)₃ O)₃ P).

Suitable bi-functional compounds include alkanolamines such as2-hydroxyethylamine, 3-hydroxypropyl- amine, 4-hydroxybutylamine,6-hydroxyhexylamine, and 2-hydroxy-1-ethylethylamine; aromatic hydroxyamines such as ortho-aminophenol; diamines such asN-methyl-1,2-diaminoethane; secondary amino alcohols such asdiethanolamine, N-methylethanolamine, N-tert butyl ethanolamine, andN,N'-diethanolethylenediamine; tertiary amino alcohols such astriethanolamine, N,N-bis (2-hydroxyethyl) cocoamine, andN,N-bis(2-hydroxyethyl) tallowamine; primary amines such as N-acetylethylene diamine; tertiary amides such as bis-[N,N-2-hydroxyethyl]dodecanamide and bis-[N,N-2-hydroxyethyl]formamide; secondary sulfidessuch as bis-[2-hydroxyethyl]sulfide and dilaurylthiodipropionate;hydrazides such as oxalic acid bis [cyclohexylidene hydrazide] (alsoknown as Cuprizon 1) and salicyl hydrazide; hydrazones such as salicylhydrazone; and oximes such as salicylaldoxime.

In selecting a suitable bifunctional compound it is important to realizethat the minimum 2 atoms which must separate the two functional atomsalso represents the preferred maximum number of interposed atoms. Thus,it is desirable that no more than 6, more desirable that no more than 5,preferred that no more than 4, more preferred that no more than 3, andmost preferred that 2 atoms separate the two functional atoms. Inmolecules with limited flexibility about the bonds (e.g.: in aromaticstructures) even three intervening atoms will cause the molecule to havelittle activity or none at all. In determining whether or not a compoundis a bifunctional compound according to the invention (i.e.: meets therequirement of being able to form a coordination complex), a usefulguide is the theoretical minimum intramolecular distance between saidfirst and second atoms. This distance is generally less than 0.48 nm,desirably less than 0.40 nm, more desirably less than 0.35 nm,preferably less than 0.30 nm, and most preferably less than 0.29 nm.Further details concerning the selection of suitable developing agentsmay be found in the aforementioned Ser. No. 068,593, which isincorporated herein by reference.

The metal particles are intermingled with the substrate by any meanswhich will achieve a distribution of particles sufficiently uniform thata conductive three-dimensional substrate can be achieved.

In the case of thermoplastic resins, the metal particles can beincorporated into the resin by melt blending or by powder blending. Inthe case of uncured resins, room-temperature blending is suitable. Anyconventional mixing apparatus is suitable.

The metal particles are contacted with the developer by any convenientmeans. One simple means is to spray a liquid developer or a solution ofa solid developer onto the metal particles before they are incorporatedinto the substrate. Another method is to blend the developing agent intothe substrate either before or after the metal particles are added. Afurther method is to add the metal to a homogeneous melt phase of thesubstrate in the developer at elevated temperature (such phases aredescribed more extensively in U.S. Pat. No. 4,519,909). In the lattercase excess developer is extracted from the polymer mixture, aftercooling, to leave a microporous, metal loaded, polymer powder which isthen suitable for typical forming operations (e.g. compression molding).A further method is to contact the metal with developer at elevatedtemperature prior to incorporation of the metal into the substrate, inaddition to or instead of adding developer to the resin. In the case ofthermosetting resins the substrate may be contacted with the metal anddeveloper by normal compounding means (e.g. 3-roll mill) either beforeor after addition of the developing agent and then subjected to aheating step in which the temperature is sufficient to render thedeveloper of the invention active, as well as a temperature sufficientto effect complete curing of the substrate.

The developer should be present in an effective amount. That is, anamount sufficient to render the metal particles conductive. Typically,the developer will be present at 1 to 200, desirably, 2 to 100,preferably 4 to 20, and more preferably 5 to 10 weight percent, based onthe weight of the metal. If the metal is pretreated with developer asdescribed above, the amount of developer in the resin can besubstantially reduced or eliminated.

Whether or not heat is used to aid the intermingling of the metal intothe substrate (as with thermoplastics), heat is necessary to activatethe developing agent. The temperature needed for activation can varywith the particular developer chosen. Generally, a temperature of 150°to 300° C., preferably 180° to 250° C., and more preferably 200° to 220°C. is required for activation.

If the developing agent is heated as part of the mixing process, thenthe heating for mixing and the heating for developing can be a singleheating step, provided that the temperature is sufficiently high foreach process.

Similarly, the heat used to cure a thermoset resin can be the heat usedto activate the developer, or the two heating steps can be distinct ifthe requisite temperatures are distinct.

The conductive substrates of the invention are useful in a wide varietyof applications including EMI shielding, battery plates, electricalswitches, and decorative panels.

The following examples are set forth to further explain the invention.

EXAMPLE 1 (COMPARATIVE)

To a 2-roll mill operating at 200° C. was added 90 g of polypropylene(Himont PD195). After "banding" (i.e.: the formation of a continuousribbon of polymer) had occurred, 60 g of copper powder (Poudmet 22BB400)was added to the polymer (to afford a formulation containing 40% ofcopper by weight), and mixing continued for 15 minutes at 200° C. Thepolymer mix was removed from the mill and subjected to compressionmolding at 215° C. under 5 tpsi (69 MPa) pressure, in a closed steelmold, for 15 minutes. After cooling a 6"×3"×0.125" (152×76.2×3.17 mm)sample was obtained with an orange appearance. The volume resistivity ofthis was measured according to DIN 53596 and found to 6×10¹⁵ ohm cm;i.e., highly non-conductive.

EXAMPLE 2

82.5 g of polypropylene, and 60 g of copper powder were mixed on atwo-roll mill as described in Example 1, but with the addition of 7.5 gof N,N-bis(2-hydroxyethyl) tallowamine (to give a formulation containing40% copper and 5% amine by weight). After mixing and molding cyclesidentical to those in Example 1, the polymer sample obtained was pink incolor and possessed a volume resistivity of 15.9 ohm cm. The presence ofan amine of the present invention had thus caused an improvement in theconductivity of copper filled polypropylene of 10¹⁴ ohm cm. In a similarmanner 30% copper and 5% of the amine by weight were incorporated; amold cycle of 30 minute at 215° C. was used. The sample possessed avolume resistivity of 0.24 ohm cm. A further reduction of the copperlevel to 25% by weight resulted in a sample with a volume resistivity of10¹⁵ ohm cm.

EXAMPLE 3

90 g of polypropylene (Himont PP 6523) and 60 g of nickel powder (Alcan756) were compounded on a two-roll mill in a manner similar to Example 1for 10 minutes at 185° C. (to give a formulation containing 40% ofnickel by weight). The polymer mix was then removed from the mill andmolded as in Example 1 for 30 minutes at 215° C. The sample obtainedpossessed a volume resistivity of 10¹⁵ ohm cm.

EXAMPLE 4

82.5 of polypropylene and 60 g of nickel powder were mixed on a two-rollmill as in Example 3, but with the addition of 7.5 g ofN,N-bis(2-hydroxyethyl) tallowamine (to give a formulation containing40% nickel and 5% amine by weight). After mixing a molding cyclesidentical to that in Example 3, the polymer sample obtained possessed avolume resistivity of 1.03 ohm cm. Thus the incorporation of a developerof the present invention results in an improvement in volume resistivityof 10¹⁵ ohm cm.

EXAMPLE 5

82.5 g of polypropylene and 60 g of copper powder were compounded on atwo-roll mill at 185° C., and 7.5 g of N,N-bis(2-hydroxyethyl)dodecanamide added. After mixing for 10 minutes the formulation(containing 40% copper and 5% amide by weight) was removed from the milland compression molded as in Example 1 but for 30 minutes at 215° C. Thespecimen obtained possessed a volume resistivity of 8.5 ohm cm. Thusamide developers of the present invention significantly improve theconductivity of copper filled polypropylene.

EXAMPLE 6 (COMPARATIVE)

Polypropylene powder (Himont PP6501) was hand blended with copper powder(Poudmet 22BB400) to afford a blend containing 40% by weight of copper.This mixture was subjected to compression molding, at 265° C. for 60minutes, in a closed cavity mold to afford a 0.125 thick plaque. Uponremoval from the mold the sample exhibited a volume resistivity inexcess of 10¹³ ohm cm.

EXAMPLE 7

The same polypropylene powder used in Example 6 was mixed in a Waringblender with 2% by weight of tributyl phosphite. The treated polymer wasthen hand mixed with copper powder to afford a blend containing 40% ofcopper by weight. The mixture was then molded as described in Example 6.The sample obtained exhibited a volume resistivity of 0.1 ohm cm and asurface resistivity of 0.1 ohm/square. The use of a phosphorus (III)compound of the present invention has thus greatly improved the volumeresistivity of the copper filled polymer.

EXAMPLE 8 (COMPARATIVE)

A. Polypropylene containing 40% by weight of copper was prepared as inExample 2, except that 5% by weight of N,N-dimethyllauramide was used inplace of N/N-bis(2-hydroxyethyl) tallowamine. After molding for 30minutes at 215° C., the sample obtained was orange in color andpossessed a volume resistivity of greater than 10¹³ ohm cm.

B. A similar polypropylene sample was prepared using 5% by weight ofcocoamine in place of the N,N-dimethyl lauramide. The volume resistivityof samples molded from this formulation were greater than 10¹³ ohm cm.

These two examples show that nitrogen containing compounds which areoutside the scope of the present invention are not effective agents forenhancing the conductivity of copper (or nickel) filled polymers.

EXAMPLE 9 (COMPARATIVE)

Polypropylene was compounded on a two roll mill at 185° C. with aluminumpowder (Alcan 2100) so as to give a mixture containing 35% aluminum byweight. After mixing for 10 minutes the polymer was removed from themill and subjected to compression molding at 230° C. for 15 minutes, anda 1/8" thick sample obtained; the sample exhibited a volume resistivityof 10⁷ ohm cm. A similar procedure was then performed to produce asample containing 35% aluminum and 5% N,N-bis(2-hydroxyethyl)tallowamine by weight. This sample possessed a volume resistivity of 10₅ohm cm. These results indicate that developers of the present inventioncannot be used to markedly enhance the conductivity of metal-filledpolymer substrates when the metal used is neither copper nor nickel.

EXAMPLE 10

High-impact polystyrene (Dow 492U) was compounded on a two-roll millwith copper powder, or with nickel powder, and withN,N-bis(2-hydroxyethyl) tallowamine using a mixing cycle of 10 minutesat 185° C. Formulations were prepared to contain 5% of amine and 40% ofeither copper or nickel by weight. After removal from the mill theformulations were subjected to compression molding for 30 minutes at215° C. in a 6"×6"×0.125" closed cavity mold. After the cooling sampleswere cut and assessed for conductivity and EMI shielding effectiveness.The copper filled sample possessed a volume resistivity of 7.5 ohm cmand shielding values of 33, 26, 27, 12 dB (at 30, 100, 300, 1000 MHz),while the values for the nickel filled polymer were 3.7 ohm cm and 39,20, 38, 33 dB. For corresponding formulations containing no amine butonly 40% by weight of either metal almost zero EMI shielding wasobserved, together with volume resistivities in excess of 10¹⁶ ohm cm.As in polypropylene the presence of developers of the present inventionin copper or nickel filled HIPS causes a dramatic improvement in bothconductivity and EMI shielding effectiveness. The conditions used abovewere not optimized.

EXAMPLE 11

Polypropylene (Himont - PP6523) was mixed with varying levels of copperor nickel and varying amounts of N,N-bis(2-hydroxyethyl) tallowamine.The mixtures were fed to a Haake twin screw extruder operating withbarrel temperatures of 165°/185°/205°/205° C. Residence time of thepolymer in the barrel was less than one minute. The extrudate in eachcase was pelletized and dried at 80° C. The extrudates were subjected tocompression molding in a closed mold at 215° C. to afford samples whichwere assessed for volume resistivity.

                  TABLE I                                                         ______________________________________                                        Wt %            Mold Time Volume Resistivity                                  Metal  Metal   Amine    (m)     (ohm cm)                                      ______________________________________                                        Cu     30      6        60      86.6                                          Cu     40      3        60      Greater than 10.sup.13                        Cu     40      6        45      0.216                                         Ni     40      3        45      Greater than 10.sup.13                        Ni     40      6        45      4.05                                          ______________________________________                                    

These results indicate that copper or nickel filled plastics containingdevelopers of the present invention can be compounded by extrusion andexhibit enhanced conductivity when compression molded.

The formulations listed above were fed to a 50 ton Newbury injectionmolding machine operating with barrel temperatures of 230°-255° C. andinjection molded at a mold temperature of 60°-65° C. and a cycle time of60 seconds to afford dogbone specimens. These specimens werenon-conductive in all cases. This may be attributed to insufficient timeat 230° C. being available for the developer to function effectively;thus when the dogbone samples were remolded in a closed cavity mold for45-60 minutes at 215° C. the nickel filled samples were converted tohigh conductivity (below 1 ohm cm).

EXAMPLE 12

The following data illustrates the effect of milling time andtemperature upon the volume resistivity, and the EMI shieldingeffectiveness of polypropylene compounded to contain 40% copper and 5%N,N-bis(2-hydroxyethyl) tallowamine. The copper and amine werecompounded into the polymer on a two-roll mill at the temperature, andfor the time, shown in the Table. The formulations were then compressionmolded in closed steel cavity molds at the temperature, and for thetime, shown in the Table. From the sample obtained a 6"×3"×01.125" thicksample was cut and used to assess volume resistivity and also EMIattenuation by the near-field method (ASTM ES7-85) at four discretefrequencies.

                  TABLE II                                                        ______________________________________                                        Roll Mill                                                                              Molding    Volume    EMI Attenuation (dB)                            Temp  Time   Temp    Time Resistivity                                                                           at MHz                                      °C.                                                                          (m)    (°C.)                                                                          (m)  (ohm cm)                                                                              30  100  300  1000                          ______________________________________                                        183   10     200     30   38      10  5    19   5                                          215     30   0.5     56  44   68   74                            193   10     200     30   6.9     10  5    19   3                                          215     30   0.4     62  46   64   79                            206   10     200     30   3.9     22  20   26   10                                         215     30   0.4     62  50   65   91                                         215     10   0.7     62  46   61   84                            206   20     200     20   3800    19  8    20   7                                          215     30   19      32  31   28   9                             ______________________________________                                    

The results illustrate that the molding cycle temperature and time areof greater importance than the milling temperature in obtaining apolymer which possess high conductivity and good EMI shieldingcharacteristics. Furthermore the data shows that too long a milling timeresults in a increase in volume resistivity and a decrease in EMIshielding effectiveness; this can be attributed to decrease in effectivesurface area of the metal filler under the influence of high shearmixing.

EXAMPLE 13

This example indicates how the molding conditions influence the EMIshielding effectiveness of a polypropylene (Himont PD195) containing 40%nickel and 5% N,N-bis(2-hydroxyethyl) tallowamine. All samples werecompounded on a two-roll mill for 10 minutes at 183° C. and thencompression molded in a closed mold under the conditions depicted in theTable.

                  TABLE III                                                       ______________________________________                                        Molding   Volume    EMI Shielding (dB)                                        Temp  Time    Resistivity                                                                             at                                                    (°C.)                                                                        (m)     (ohm cm)  30   100   300  1000  MHz                             ______________________________________                                        180   60      10.sup.14 0    0     6    1                                     200   60      0.4       51   40    56   55                                    200   30      26.0      41   29    40   24                                    200   15      10.sup.14 1    0     6    0                                     215   60      0.2       61   57    67   80                                    215   30      0.3       59   52    64   65                                    215   15      1.1       42   31    45   32                                    230   15      0.2       61   60    72   82                                    230   10      0.2       62   57    67   78                                    230   5       0.3       60   53    65   74                                     230* 15      10.sup.13 0    0     6    1                                     ______________________________________                                         *Sample did not contain N,N,bis (2hydroxyethy1) tallowamine              

The data clearly illustrates that good conductivity and high EMIshielding for nickel filled formulation are only achieved in thepresence of a developer of the present invention, and that there is anoptimum molding (temperature and time) cycle. As the molding temperatureincreases the time required to obtain good EMI shielding becomesreduced. Obviously the amine developer becomes more effective at highermolding temperatures. Optimum conditions may be expected to varysomewhat with the polymer used.

EXAMPLE 14

Samples of polypropylene containing 40% nickel and 5%N,N-bis(2-hydroxyethyl) tallowamine by weight obtained under the variousmolding conditions described in Example 13 were placed in an air over at90° C. and reassessed for EMI shielding at intervals. The results areshown in Table IV.

                                      TABLE IV                                    __________________________________________________________________________           Final                                                                  Molding                                                                              Volume                                                                              EMI Shielding (dB)                                               Temp                                                                              Time                                                                             Resistivity                                                                         at 30/100/300/1000 MHz                                           (°C.)                                                                      (m)                                                                              (ohm cm)                                                                            Original                                                                             After 7 Days                                                                         14 Days                                                                              21 Days                                     __________________________________________________________________________    200 60 150   51/40/56/55                                                                          35/21/27/15                                                                          17/11/24/10                                                                          Not measured                                200 30 1.9 × 10.sup.6                                                                41/29/40/24                                                                          8/3/17/6                                                                             1/0/9/3                                                                              Not measured                                215 60 4.5   61/57/67/80                                                                          51/42/58/55                                                                          46/35/50/36                                                                          43/30/44/26                                 215 30  68   59/52/64/65                                                                          38/27/36/18                                                                          20/10/22/9                                                                           Not measured                                215 15 4300  42/31/45/32                                                                          28/19/27/14                                                                          1/0/13/4                                                                             Not measured                                230 15 3.7   61/60/72/82                                                                          51/42/60/61                                                                          47/36/50/43                                                                          44/31/43/32                                 230 10 4.3   62/57/67/78                                                                          52/44/57/38                                                                          43/36/45/24                                                                          Not measured                                230 5  8.9   60/53/65/74                                                                          43/32/45/26                                                                          35/28/36/17                                                                          Not measured                                __________________________________________________________________________

The results reveal that the original molding conditions chosen affectnot only the initial EMI shielding effectiveness but also the rate ofloss of EMI shielding. Higher molding temperature/times decrease therate of loss of EMI shielding when the formulation is aged attemperatures above ambient.

EXAMPLE 15

Polypropylene was mixed with varying amounts of nickel powder and alsowith varying amounts of N,N-bis-(2-hydroxyethyl)tallowamine on atwo-roll mill. After mixing for 10 minutes at 185° C. the formulationswere compression molded in a closed mold for 15 minutes at 230° C. toafford 1/8" thick samples which were assessed for volume resistivity andEMI shielding. The results are shown in Table V.

                  TABLE V                                                         ______________________________________                                                  Volume     EMI Shielding (dB)                                       Wt %      Resistivity                                                                              at                                                       Nickel                                                                              Amine   (ohm cm)   30   100  300  1000  MHz                             ______________________________________                                        40    5       0.22       61   60   72   82                                    35    5       0.33       58   52   64   77                                    30    5       0.28       57   51   63   77                                    25    5       10.sup.13  0    0    0    0                                     40    3       0.42       54   47   64   62                                    40    2       1.6        49   40   55   51                                    40    1       1.3        50   39   52   65                                    ______________________________________                                    

The data demonstrates that good conductivity and high EMI shielding canbe obtained from nickel filled polypropylene with 30% or more by weightof nickel. Furthermore at the 40% by weight of nickel level, 1% byweight of the amine developer is sufficient to promote conductivity;higher levels of amine effect somewhat better nickel conductivity andhigher EMI shielding values, and may be preferred.

EXAMPLE 16

To polypropylene (Himont PP 6523) were added the levels of metallicpowder and N,N-bis(2-hydroxyethyl)tallowamine detailed below. Themixtures were passed through a Haake twin-screw extruder operating withzone temperatures of 165°/185°/205°/200° C. (barrel temperature) toafford 1/8" thick tensile (dogbone) specimens. For each formulation thetensile strength was measured on an Instron machine before aging, and onsamples withdrawn after 1, 2, 3 and 4 weeks of aging in an oven held at90° C. The results of the tensile strength measurements are shown in theTable.

From the results it can be seen that whereas the presence of copper inthe formulation results in a dramatic loss of tensile strength upon ovenaging, the presence of nickel does not cause any significant loss oftensile strength. Note also that the presence of the particulardeveloper used has a retarding effect upon the rate of loss of tensilestrength for formulations which contain copper; this may be because ofthe ability of the developer to coordinate to copper atoms and thusreduce the number of such species available for catalysis of theautoxidation process. The decrease in the unaged tensile stength forformulations containing the developer can be attributed to the developeracting as a plasticizer.

From these results it can be seen that nickel-filled thermoplasticsprocessed according to the present invention will probably be preferredover copper-filled thermoplastics if the end-formulation is likely to besubjected to extended use at higher temperatures.

                  TABLE VI                                                        ______________________________________                                                                 % Original Tensile                                                   Original Strength Retained                                                    Tensile  After Oven Aging                                     Wt %            Strength At 90° C. for Weeks                           Metal Metal   Developer (PSI)  1    2    3    4                               ______________________________________                                        Cu    30      --        4151   95   57.8 25.6 2.6                             Cu    30      3         3119   104.5                                                                              71.4 40.2 7.5                             Cu    30      6         2810   103.1                                                                              80.4 56.5 40.6                            Cu    40      --        3230   102.2                                                                              54.2 16.1 2.6                             Cu    40      3         2700   105.0                                                                              67.1 30.4 5.6                             Cu    40      6         2172   115.0                                                                              110.8                                                                              61.8 15.0                            Ni    30      --        4010   105.8                                                                              108.3                                                                              102.8                                                                              107.7                           Ni    30      3         3019   106.4                                                                              110.5                                                                              107.2                                                                              110.7                           Ni    30      6         2639   109.7                                                                              116.2                                                                              115.4                                                                              119.3                           Ni    40      --        3774   106.1                                                                              105.7                                                                              107.9                                                                              106.1                           Ni    40      3         2822   106.1                                                                              111.1                                                                              112.6                                                                              111.3                           Ni    40      6         2714   102.2                                                                              109.3                                                                              106.5                                                                              108.6                           ______________________________________                                    

EXAMPLE 17

Nylon 6 (Zytel 211, DuPont) formulations containing various levels ofnickel powder (Alcan 756), and of N,N-bis (2-hydroxyethyl) tallowamine,were prepared by supplying a dry blend of the mixtures to the throat ofa Haake twin-screw extruder operating with barrel/die temperatures of195°/215°/230°/220° C. The extrudate was pellatized and dried. Thepellets were compression molded in a 6"×6"×1/8" (152×152×3.2 mm) closedsteel cavity mold for the times, and at the temperatures shown in theTable. After removal from the mold, 3"×6"×1/8" (76×152×3.2 mm) sampleswere cut and assessed for volume resistivity and for EMI attenuation(near-field); the results obtained are shown in Table VII.

                                      TABLE VII                                   __________________________________________________________________________                       Volume                                                                              EMI Attenuation (dB)                                 Wt %                                                                              Wt %                                                                              Molding                                                                             Molding                                                                            Resistivity                                                                         at                                                   Nickel                                                                            Amine                                                                             Temp (°C.)                                                                   Time (m)                                                                           ohm cm                                                                              30                                                                              100                                                                              300                                                                              1000                                                                             MHz                                       __________________________________________________________________________    30  0   240   27   2.5 × 105                                                                     01                                                                              04 06 00                                           30  0   240   45   10.sup.13                                                                           10                                                                              03 15 04                                           35  0   240   27   10.sup.13                                                                           00                                                                              00 06 00                                           35  0   240   40   10.sup.13                                                                           00                                                                              00 06 01                                           30  2.5 240   27   2.4   42                                                                              28 39 20                                           30  2.5 240   45   0.24  64                                                                              56 72 74                                           35  2.5 240   17   0.24  62                                                                              54 65 82                                           35  2.5 230   15   0.22  64                                                                              56 70 75                                           30  5.0 240   27   0.23  62                                                                              55 67 78                                           30  5.0 225   15   1.6   43                                                                              30 44 19                                           35  5.0 240   20   0.21  63                                                                              73 77 88                                           35  5.0 240   15   0.18  64                                                                              63 77 90                                           __________________________________________________________________________

It can be seen that in the absence of the amine developer of the presentinvention formulations containing 30 or 35% of nickel powder exhibithigh volume resistivity and very low EMI attenuation. In contrast,samples containing the amine developer, molded under identicalconditions, exhibit low volume resistivity and high EMI attenuation. Asmetal and/or developer level in the formulation increases lower moldingtimes/temperatures are required to achieve high levels of EMIattenuation and volume conductivity.

EXAMPLE 18

Nylon 6 extrudates, containing various levels of nickel powder and ofN,N-bis (2-hydroxyethyl) tallowamine, produced as described in Example17 were injection molded on a Newbury 50 ton reciprocating screw machinefitted with a 4"×3"×1/16" (102×76×1.6 mm) mold cavity. Variousbarrel/die temperature regimes were employed, together with differentoverall cycle times (Note: on the machine used the polymer formulationis exposed to barrel temperature for approximately eight times the cycletime). After molding, the samples were evaluated for volume resistivity.The results are shown in the Table VIII.

                  TABLE VIII                                                      ______________________________________                                        Wt %  Wt %    Cycle    Barrel/Die                                                                             Volume Resistivity                            Ni    Amine   Time (s) Temp (°C.)                                                                      ohm cm                                        ______________________________________                                        35    0       90       245/260/260                                                                            1.4 × 10.sup.7                          35    2.5     90       235/250/250                                                                            7.6 × 10.sup.7                          35    2.5     90       240/255/255                                                                            3.0 × 10.sup.7                          35    2.5     90       245/260/260                                                                            1.5                                           35    1.0     90       245/260/260                                                                            0.2                                           35    1.0     60       245/260/260                                                                             0.48                                         25    2.5     90       245/260/260                                                                            10.sup.13                                     ______________________________________                                    

It can be noted that enhancement of the volume conductivity by the useof the amine developer of the present invention requires the use of asuitable barrel/die temperature profile and suitable cycle time. Theseparameters may vary with the design of the injection molding machineused but can be determined experimentally.

EXAMPLE 19

Noryl (N225/78, General Electric) formulations containing various levelsof nickel powder (Alcon 756) and of N,N-bis (2-hydroxyethyl) cocoaminewere prepared by extrusion in a similar fashion to that described inExample 17. The pellets obtained were compression molded. The moldingtemperatures and times used, and the volume resistivities and EMIattenuations measured are shown in the Table below IX.

                                      TABLE IX                                    __________________________________________________________________________                       Volume                                                                              EMI Attenuation (dB)                                 Wt %                                                                              Wt %                                                                              Molding                                                                             Molding                                                                            Resistivity                                                                         at                                                   Ni  Amine                                                                             Temp (°C.)                                                                   Time (m)                                                                           ohm cm                                                                              30                                                                              100                                                                              300                                                                              1000                                                                             MHz                                       __________________________________________________________________________    35  0   225   27   10.sup.13                                                                           00                                                                              00 01 00                                                   240   60   10.sup.13                                                                           00                                                                              00 02 00                                                   255   20   10.sup.13                                                                           00                                                                              00 04 00                                           35  5   225   27   10.sup.13                                                                           00                                                                              00 05 01                                                   240   60   7.7   35                                                                              29 30 11                                                   255   20   0.2   57                                                                              52 70 72                                           40  5   257   15    0.21 52                                                                              43 55 63                                           __________________________________________________________________________

Again it is clear that an amine developer of the present inventioneffects a dramatic increase in the volume conductivity and EMIattenuation of nickel filled polyphenylene oxide formulations. Also notethat the molding temperature has to be sufficiently high to allow theamine developer to function effectively in a reasonable time.

EXAMPLE 20

Formulations of polybutylene terephthalate (PBT) containing 30% glassfiber (Valox 420, General Electric) were compounded as described inExample 17 to contain various levels of nickel filler and various levelsof N,N-bis (2-hydroxyethyl) lauramide. The pellets obtained werecompression molded for the times, and at the temperatures, shown in theTable below. The values for EMI attenuation and volume resistivitymeasured are also depicted in Table X.

                                      TABLE X                                     __________________________________________________________________________                       Volume                                                                              EMI Attenuation (dB)                                 Wt %                                                                              Wt %                                                                              Molding                                                                             Molding                                                                            Resistivity                                                                         at                                                   Ni  Amine                                                                             Temp (°C.)                                                                   Time (m)                                                                           ohm cm                                                                              30                                                                              100                                                                              300                                                                              1000                                                                             MHz                                       __________________________________________________________________________    35  0   245   22   10.sup.13                                                                           01                                                                              00 14 05                                           35  1   245   22   0.78  47                                                                              37 50 40                                           30  1   250   27   0.42  52                                                                              46 58 48                                           30  1   245   27   0.79  46                                                                              34 47 40                                           25  1   245   27   2.0   40                                                                              30 39 19                                           20  1   250   27   10.sup.13                                                                           04                                                                              03 16 03                                           __________________________________________________________________________

Hence an amide developer of the present invention is able to effect alarge increase in the volume conductivity and EMI attenuation of aglass-reinforced, nickel filled, polyester formulation. Because of thediluent effect of the glass reinforcement reasonable conductivity couldbe achieved by the use of the developer at somewhat lower weight %nickel loadings than in unreinforced nickel filled thermoplastics.

EXAMPLE 21

A glass reinforced PBT (Valox 420) formulation was compounded, asdescribed above, to contain 30% by weight of nickel powder and 1% byweight of N,N-bis-(2-hydroxyethyl) lauramide. The resulting pellets wereused to produce injection molded specimens using barrel/die temperaturesof 250°/270°/270° C. and a cycle time of 90 seconds. When assessed forvolume resistivity the molded specimens gave values of approximately 2.5to 4.5 ohm·cm; i.e., the specimens possessed good volume conductivity.

EXAMPLE 22

200 g of N,N-bis(2-hydroxyethyl)tallowamine were heated to 190°-200° C.while being stirred with a high shear type stirrer blade. To this wasadded in portions, 60 g of polypropylene. After 10-15 minutes at 200° C.the polypropylene had melted and become dispersed into the amine toyield a homogenous viscous fluid. To this was added 40 g of copperpowder. Stirring was continued for 2 minutes after attaininghomogeniety. The whole mixture was then poured quickly into a cold dishso that rapid cooling and solidification occurred. The solid was choppedinto pieces and ground in a food blender in the presence of isopropanol(this solvent extracts the amine to leave a copper loaded microporouspolymer such as described in U.S. Pat. No. 4,519,909; scanning electronmicroscopy confirmed the presence of microporous polypropylene). Afterrecovering the Cu loaded polymer by filtration, it was washed repeatedwith isopropanol until the washings were colorless. The polymer was thendried 4 hours at 50° C. to remove the solvent. These copper loaded PPgranules were then compression molded at 215° C. for 17 minutes under 5tpsi (69 MPa) pressure and 3"×6"×0.125" (152×76.2×3.17 mm) samplesobtained. The volume resistance was measured as 0.8 ohm cm, indicatingthat this procedure for producing a microporous copper filledpolypropylene results in material exhibiting excellent conductivity. Thesamples molded also exhibited greater than 40 db of EMI attenuation whenassessed by the near field method according to ASTM ES7-85.

In similar experiments the weight % loading of copper in polypropylenewas reduced from the 40% used above, to 35% and 30% by weight. Volumeresistance of samples molded from such material was 0.8 and 0.13 ohm cmrespectively.

EXAMPLE 23

Microporous polypropylene was prepared by the procedure outlined inExample 20, except that 40% by weight of nickel flake (Alcan 756) topolypropylene was used in place of the copper powder. Molded sampleswere observed to possess volume resistances of 13 to 250 ohm cm.

EXAMPLE 24

Equal weights of an epoxy resin (Shell Epon 828) and a hardener (DowVersamid 125) were mixed together. Copper powder (Poudmet 22BB400) wasadded slowly to the mixture, with hand mixing, so as to afford aformulation which contained resin:hardener:copper in weight ration of15:15:70. The copper filled resin was divided into two equal portions.To one portion was added and mixed in an amount ofN,N-bis(2-hydroxyethyl) cocoamine equivalent to 5% by weight of thecopper powder contained therein. Each portion was then transferred to analuminum dish and allowed to stand at room temperature for 8 hours;during this time the epoxy resin became cured via the action of thehardener and the nature of the samples changed from fluid to solid. Uponremoval of the cured portions from the trays neither exhibited anyindication of conductivity when tested with a 2-probe ohmmeter. Eachportion was cut into 2 halves. One half from each portion was placed inseparate glass vessels, which were thereafter evacuated to below 1 mm Hgof pressure. The vessels were sealed and heated in an oven at 220° C.for 30 minutes, then removed, cooled to ambient, and the samples removedand reassessed for conductivity by the use of a 2-probe ohmmeter. Againneither specimen exhibited any measurable conductivity. Theseexperiments indicate that the addition of a developer of the presentinvention to the particular epoxy (Thermoset) resin used and containing50 to 70% by weight of copper does not result in enhanced conductivity.This is in contrast to the results described for thermoplastics in theExamples above; a complete explanation for the non-enhacement ofconductivity of the copper-filled epoxy resin by the developing agent isnot available; however, encapsulation of the individual copper particlesby the fluid uncured resin is one possible reason. It is likely thatmore extensive formulation work with a variety of other thermosettingplastics (epoxy and non-epoxy types) would reveal conditions under whichcopper filled thermosetting resins could be rendered more conductive bythe use of developers of the present invention.

We claim:
 1. A method of forming a conductive metal-filled substrate,comprising:a. an intermingling step of intermingling metal particles ina deformable substrate, wherein the metal particles are selected fromthe group consisting of copper, nickel, and combinations thereof, andare intermingled in a quantity sufficient to achieve a conductivethree-dimensional substrate; b. a contacting step of contacting themetal particles with a developing agent comprising a material selectedfrom the group consisting of a long-chain aliphatic tertiary amine; atertiary phosphine or a tertiary phosphite; and a bifunctional compoundhaving both (1) a first atom which is a trivalent nitrogen atom or abivalent sulfur atom and (2) at least one second atom which is nitrogenor oxygen, the first and second atoms being separated by at least twoother atoms, the bifunctional compound being capable of forming acoordination complex with copper or nickel; and c. a heating step ofsubjecting the metal particles and the developing agent to heat, in thesubstantial absence of oxygen, at a temperature and for a durationsufficient to improve the conductivity of the metal-filled substrate. 2.The method of claim 1 wherein said intermingling step comprises meltblending the metal particles into the substrate.
 3. The method of claim1 wherein said intermingling step comprises blending the metal particlesinto an uncured resin at ambient temperature.
 4. The method of claim 1wherein the copper or nickel contains less than about 40 weight % ofnonconductive substrate forming metals.
 5. The method of claim 1 whereinthe copper or nickel contains less than about 20 weight % ofnonconductive substrate forming metals.
 6. The method of claim 1 whereinthe metal particles have a number average particle size of less thanabout 30 um.
 7. The method of claim 1 wherein the metals are present inthe form of an mixture containing less than about 25 weight % of othernonconductive-substrate forming metals.
 8. The method of claim 1 whereinsaid heating step takes place at temperature below the melting point ofany substantially present metal.
 9. The method of claim 1 wherein saidheating step takes place at or above the softening point of thesubstrate.
 10. The method of claim 1 wherein the substrate is asynthetic resin.
 11. The method of claim 10 wherein the substrate is athermoplastic resin.
 12. The method of claim 1 wherein said contactingstep comprises contacting the developing agent in liquid form with themetal particles prior to said intermingling step.
 13. The method ofclaim 1 wherein said contacting step and said heating step take placeprior to said intermingling step.
 14. The method of claim 1 wherein saidcontacting step comprises incorporating the developing agent into thesubstrate prior to said intermingling step.
 15. The method of claim 1wherein said contacting step comprises incorporating the developingagent into the substrate simultaneous with said intermingling step. 16.The method of claim 1 wherein said contacting step comprisesincorporating the developing agent into the substrate subsequent to saidintermingling step.
 17. The method of claim 1 wherein the developingagent is a tertiary amine.
 18. The method of claim 17 wherein thetertiary amine has at least on C₈ to C₂₀ alkyl group.
 19. The method ofclaim 18 wherein the at least one C₈ to C₂₀ alkyl group is a coco,tallow, or hydrogenated tallow group.
 20. The method of claim 19 whereinthe tertiary amine also contains a hydroxyalkyl group.
 21. The method ofclaim 20 wherein the tertiary amine is N,N bis(2-hydroxyethyl)cocoamineor N,N-bis(2-hydroxyethyl)tallow amine.
 22. The method of claim 1wherein the developing agent is a tertiary phosphine or a tertiaryphosphite.
 23. The method of claim 1 wherein the developing agent is abifunctional compound.
 24. The method of claim 23 wherein thebifunctional compound is a chelant for copper or nickel.
 25. The methodof claim 23 wherein said first and second atoms have a minimumtheoretical intramolecular distance of less than 0.40 nm.
 26. The methodof claim 23 wherein said first atom is nitrogen.
 27. The method of claim23 wherein the bifunctional compound is an alkanolamine or a diamine.28. The method of claim 26 wherein said bifunctional compound is adi(hydroxyalkyl) tertiary amide.
 29. The method of claim 28 wherein saiddi(hydroxyalkyl) tertiary amide is a di(2-hydroxyethyl)alkyl amidehaving 5 to 20 carbons in the alkyl moity.
 30. The method of claim 29wherein said di(2-hydroxyethyl) alkyl amide isdi(2-hydroxyethyl)dodecanamide.